(1) Field of the Invention
This invention relates to a propylene polymer composition which may be suitably used as extrusion molding, injection molding and blow molding materials in the fields of car parts, home electric appliances, and so forth.
(2) Description of the Prior Art
Commercial propylene-ethylene copolymers referred to as "propylene block copolymers" are used favorably as resins of excellent impact resistance and rigidity in many industrial fields. However, there have been problems in their application for articles whose appearance is important, such as car parts and home electric appliances because, receiving impact, etc., the appearance of molding products tends to be suffered by whitening at the stress point due to their deficiency in whitening resistance.
In the past, methods of blending polyethylene with propylene copolymers were proposed to solve said problems (c. f. Japanese Patent Laid-open No. 58245/1980 and Japanese Patent Laid-open No. 13741/1982), but these methods were not sufficient in improvement of the impact whitening resistance, and had difficulty in homogenious blending. Another method for producing propylene copolymers by two stage polymerization was proposed (c.f. Japanese Patent Laid-open No. 55416/1981), but obtained products had no sufficient in the balance of impact resistance, rigidity and whitening resistance.
On the other hand, a method for modification of propylene copolymers by heat-treatment to improve the flowability was known (c.f. Japanese Patent Laid-open No. 76444/1983), but there was the defect that flowability and mechanical properties were not balanced.